In conventional positron emission tomography (PET) cameras, it is conventional to use a single light detector, such as a photomultiplier tube, coupled to a single scintillator crystal. However, it has been proposed in U.S. Pat. No. 4,563,582 and Great Britain Pat. No. 1,406,685 that it is advantageous to use a greater number of scintillator crystals for obtaining a more efficient and less expensive PET camera by coupling a photomultiplier tube to a plurality of scintillator crystals in which the identification of the individual crystals can be decoded by a smaller number of photomultiplier tubes. However, in some of the schemes, the crystals have to be located outside a specific plane and form a zig-zag detector ring which lowers the axial resolution or lowers the angular sampling in any cross-sectional plane which limits the ratio of crystals/PMT. Also, since the photomultiplier tubes and the crystal scintillators each have a dead space at their outer boundaries caused by boundary layers for guiding the detected radiation and light, the ratio of the number of crystals to a photomultiplier tube is limited. However, it is advantageous in a PET camera to utilize a greater number of smaller crystals for providing a greater efficiency and for eliminating the conventional mechanical wobbling of the camera by providing finer sampling by using a greater number of small crystals.
The present invention is directed to providing a plurality of slanting light guides to transfer light from the crystal scintillators to allow a minimum of light detectors to be used to decode the position of the scintillations detected by a multitude of small crystals regardless of the position of the crystals. The slanting light guides provide a coupling between the crystals and the light detectors with very high optical efficiency since the light output from each crystal only goes to a single light guide thereby reducing scatter from the crystals. The efficiency is also enhanced by having the area and shape of the entrance and exit ends of the light guides substantially the same. The light guides are arranged in a configuration to provide a high ratio of crystals to detectors.